Myocastor coypus, a rapidly breeding, super-destructive Argentinean swamp rat that grows as big as a medium-sized dog, was found days ago on Roberts Island.

“This discovery throws us for a loop,” said Peter Tira, a spokesman for the California Department of Fish and Wildlife.

That’s because the northernmost detection of this invasive, semi-aquatic, 20-pound rodent had been Stanislaus County. DFW was concentrating eradication efforts further south. The idea was to head the nutria off from reaching the Delta.

Swamp rat 1, DFW 0. Go, defense!

Some may shrug. The Delta’s full of invasive species, so what’s another? Tira counters that nutria pose a grave threat.

“There are invasive species, and then there are nutria,” Tira said. “They’re the triple threat, we call ’em, in terms of invasive species.”

Because Nutria eat aquatic roots, and crops, and they burrow into levees.

As for aquatic plants, nutria destroy far more than they eat, tearing plants out with forepaws as they stuff their faces with one-quarter of their body weight a day.

Without roots to bind soil, wetlands dissolve into open water. Yet wetlands are key to native Delta species, some of which are endangered or threatened.

Not to mention crops. The mainstay of San Joaquin’s economy. Cattle, too, may be harmed by parasites that nutria poop into water. Humans, too.

Nutria resemble beaver — except for round, ratlike tails and vivid, almost glowing orange front teeth (who has orange teeth?) but instead of building dens, they bore into levees.

To top it off, a mama nutria gives birth two or three times a year, up to 13 young per litter. The young soon breed. Nutria multiply exponentially.

And the Delta has none of their natural Argentine predators: the cayman, the jaguar. Nor does it have cold weather that retards their spread elsewhere.

Faced with this crisis, “Our goal is complete eradication in California,” Tira said.

DFW has divided the state into 40 grids and created GIS maps of detections and other data. Oops, the nutria migrated northward off the grid.

And not to the “edge of the Delta” as reported elsewhere. Roberts Island is in the “legal Delta,” the core within the secondary zone.

DFR is training a dozen wildlife biologists for battle. They are planting waterproof cameras around the Delta and baiting traps with sweet potatoes. Other agencies are joining the fight.

The plan calls for more cameras, more traps, presumably a bigger grid and perhaps scent-trained dogs.

But not bounty hunting. Nutria look too much like beavers or muskrats. Officials fear hunters will blast native animals.

The good news: “We believe we’re in the early phase” of infestation, Tira said. The bad news: Given the nutria’s rapid population growth, the battle may be won or lost in the early phase.

State Sen. Cathleen Galgiani, D-Stockton, wants to hold hearings “to find out the extent of the problem, who’s doing what and what more can be done,” said Robin Adam, a senior consultant to the senator.

“Cathleen is extremely concerned about this,” Adam added.

One wonders, can government ward off the nutria?

“We’re marshaling every resource we can,” Tira said. “We have some of our best and brightest on this project.”

Restore the Delta’s Barbara Barrigan-Parilla said she fears that the state may exploit the nutria problem to advance its Delta tunnels agenda.

“If they can show there are problems with levees from nutria burrowing into levees then there’s a case that the state can make for the project,” Barrigan-Parilla said. “That’s what terrifies me.”

Granted, there’s something almost ridiculous about being menaced by a giant swamp rat. Bill Jennings of the California Sportfishing Protection Alliance saw the humor in it.

“The Delta has a long history of invasion by rats,” he said, “from the Bureau of Reclamation to the DWR (Department of Water Resources) to the Metropolitan Water District. I would put it into a lesser category than those. But it’s still a big rat.”

It’s a big rat which will rapidly become the bane of the Delta — an ineradicable, six-figure infestation, a pestilence to Ag, a blow to the economy, a threat to state water conveyance and even to public safety (think levee breaks) — unless authorities urgently mobilize.

No kidding.

“It’s touch and go,” said Tira. “We really believe California’s future as we imagine it is at stake here.”